1. Field of the Invention
The present invention relates to an objective optical system with a high numerical aperture and a long, thin shape, and more particularly, to a liquid-immersion objective optical system that is suitable for insertion into an animal, such as a mammal, for in-vivo examination.
This application is based on Japanese Application No.2004-199632, the content of which is incorporated herein by reference.
2. Description of Related Art
Conventional methods include those in which a dye or fluorescent marker is attached to particular molecules, tissue, or cells, which are then examined using a fluorescence microscope, a confocal laser-scanning microscope, or the like, to observe the behavior of the molecules inside the cells or tissue of a living organism. Since the behavior of molecules in the body of a live mammal, such as a mouse, may differ from that in cultured cells, it is usual to carry out in-vivo examination of biological tissue and cells in a living organism.
Since conventional microscopes have a large objective lens diameter, when examining the interior of a body of a living organism, it is necessary to make a large incision in the living organism for examination. However, since making a large incision in the organism results in a high degree of invasiveness, an excessively large strain is placed on the organism, and therefore, it is not possible to carry out examination for a long period of time.
Endoscopes generally have a small diameter, resulting in a low level of invasiveness to the organism; however, since their magnification is low, the behavior of molecules in the tissue and cells of the organism cannot be sufficiently examined.
Furthermore, magnifying endoscopes have a higher magnification but the numerical aperture (NA) at the object side is low. Therefore, the resolution and brightness are insufficient.
In the specification of US Patent Application No. 2004/0051957, an objective optical system having a high numerical aperture, a narrow diameter, and a comparatively long overall length is disclosed. With this objective optical system, it is possible to examine a living organism with a low degree of invasiveness by making a small hole in the organism and inserting the objective optical system through this hole.
However, the objective optical system disclosed in the above-cited reference has a drawback in that chromatic aberrations are not sufficiently corrected. Therefore, when performing white-light observation and fluoroscopy, since the wavelength of fluorescence produced in the specimen is different from the wavelength of the excitation light, the resolution is reduced. When performing fluoroscopy, particularly when using a confocal optical system, if the chromatic aberrations are not corrected, there is a problem in that the brightness of the fluorescence to be detected is low.